Inductively coupled plasma apparatus

ABSTRACT

Methods and apparatus for plasma processing are provided herein. In some embodiments, a plasma processing apparatus includes a process chamber having an interior processing volume; a first RF coil disposed proximate the process chamber to couple RF energy into the processing volume; and a second RF coil disposed proximate the process chamber to couple RF energy into the processing volume, the second RF coil disposed coaxially with respect to the first RF coil, wherein the first and second RF coils are configured such that RF current flowing through the first RF coil is out of phase with RF current flowing through the RF second coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 12/821,609, filed Jun. 23, 2010, which claims benefit of U.S.provisional patent application Ser. No. 61/254,833, filed Oct. 26, 2009.Each of the aforementioned related patent applications is hereinincorporated by reference.

FIELD

Embodiments of the present invention generally relate to plasmaprocessing equipment.

BACKGROUND

Inductively coupled plasma (ICP) process reactors generally form plasmasby inducing current in a process gas disposed within the process chambervia one or more inductive coils disposed outside of the process chamber.The inductive coils may be disposed externally and separatedelectrically from the chamber by, for example, a dielectric lid. Whenradio frequency (RF) current is fed to the inductive coils via an RFfeed structure from an RF power supply, an inductively coupled plasmacan be formed inside the chamber from an electric field generated by theinductive coils.

In some reactor designs, the reactor may be configured to haveconcentric inner and outer inductive coils. The inventors havediscovered that additive electric field properties (due to destructiveinterference of the magnetic fields induced by the coils) between theinner and outer coils can result in non-uniformities in the electricfield distribution of the plasma formed at the substrate level away fromthe coils. For example, due to etch rate non-uniformities caused by thenon-uniform electric field distribution in the plasma, a substrateetched by such a plasma may result in a non-uniform etch pattern on thesubstrate, such as an M-shaped etch pattern, e.g., a center low and edgelow etch surface with peaks between the center and edge. The inventor'shave further observed that adjusting the power ratio between the innerand outer coils to control the severity of the non-uniformity is notsufficient to completely eliminate the non-uniformity. Moreover, inorder to meet the critical dimension requirements of advanced devicenodes, e.g., about 32 nm and below, the remaining etch patternnon-uniformities due to this phenomenon may need to be further reducedor eliminated.

Accordingly, the inventors have devised a plasma process apparatus tobetter control plasma processing non-uniformity.

SUMMARY

Methods and apparatus for plasma processing are provided herein. In someembodiments, a plasma processing apparatus includes a process chamberhaving an interior processing volume; a first RF coil disposed proximatethe process chamber to couple RF energy into the processing volume; anda second RF coil disposed proximate the process chamber to couple RFenergy into the processing volume, the second RF coil disposed coaxiallywith respect to the first RF coil, wherein the first and second RF coilsare configured such that RF current flowing through the first RF coil isout of phase with RF current flowing through the second RF coil.

In some embodiments, a plasma processing apparatus includes a processchamber having an interior processing volume; a first RF coil disposedproximate the process chamber to couple RF energy into the processingvolume and wound in a first direction; and a second RF coil disposedproximate the process chamber to couple RF energy into the processingvolume, the second RF coil disposed coaxially with respect to the firstRF coil and wound in a second direction opposite the first directionsuch that RF current flows through the first RF coil in the firstdirection and through the second RF coil in the second direction.

In some embodiments, a method of forming a plasma includes providing anRF signal through a first RF coil; providing the RF signal through asecond RF coil coaxially disposed with respect to the first RF coil suchthat the RF signal flows through the second coil out of phase withrespect to the flow of the RF signal through the first coil; and forminga plasma by coupling the RF signal provided by the first and second RFcoils to a process gas disposed in a process chamber. Other and furtherembodiments of the present invention are described below.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention, briefly summarized above anddiscussed in greater detail below, can be understood by reference to theillustrative embodiments of the invention depicted in the appendeddrawings. It is to be noted, however, that the appended drawingsillustrate only typical embodiments of this invention and are thereforenot to be considered limiting of its scope, for the invention may admitto other equally effective embodiments.

FIG. 1 depicts a schematic side view of an inductively coupled plasmareactor in accordance with some embodiments of the present invention.

FIG. 2 depicts a schematic top view of a pair of RF coils of aninductively coupled plasma reactor in accordance with some embodimentsof the present invention.

FIGS. 3A-B illustratively depict graphs of etch rate profiles generatedusing conventional apparatus and an embodiment of the inventiveapparatus as disclosed herein.

FIGS. 4A-B depict an RF feed structure in accordance with someembodiments of the present invention.

FIGS. 5A-B depict schematic top views of an inductively coupled plasmaapparatus in accordance with some embodiments of the present invention.

FIG. 6 depicts a flow chart for a method of forming a plasma inaccordance with some embodiments of the present invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Methods and apparatus for plasma processing are provided herein. Theinventive methods and plasma processing apparatus advantageously providea more uniform plasma as compared to conventional apparatus, thusproviding a more uniform processing result on a substrate beingprocessed with the plasma. For example, a plasma formed utilizing theinventive plasma apparatus has an improved electric field distribution,which provides a more uniform plasma and can be utilized to produce amore uniform process, such as an etch pattern on a surface of asubstrate.

FIG. 1 depicts a schematic side view of an inductively coupled plasmareactor (reactor 100) in accordance with some embodiments of the presentinvention. The reactor 100 may be utilized alone or, as a processingmodule of an integrated semiconductor substrate processing system, orcluster tool, such as a CENTURA® integrated semiconductor waferprocessing system, available from Applied Materials, Inc. of SantaClara, Calif. Examples of suitable plasma reactors that mayadvantageously benefit from modification in accordance with embodimentsof the present invention include inductively coupled plasma etchreactors such as the DPS® line of semiconductor equipment (such as theDPS®, DPS® II, DPS® AE, DPS® G3 poly etcher, DPS® G5, or the like) alsoavailable from Applied Materials, Inc. The above listing ofsemiconductor equipment is illustrative only, and other etch reactors,and non-etch equipment (such as CVD reactors, or other semiconductorprocessing equipment) may also be suitably modified in accordance withthe present teachings.

The reactor 100 includes an inductively coupled plasma apparatus 102disposed atop a process chamber 104. The inductively coupled plasmaapparatus includes an RF feed structure 106 for coupling an RF powersupply 108 to a plurality of RF coils, e.g., a first RF coil 110 and asecond RF coil 112. The plurality of RF coils are coaxially disposedproximate the process chamber 104 (for example, above the processchamber) and are configured to inductively couple RF power into theprocess chamber 104 to form a plasma from process gases provided withinthe process chamber 104.

The RF power supply 108 is coupled to the RF feed structure 106 via amatch network 114. A power divider 105 may be provided to adjust the RFpower respectively delivered to the first and second RF coils 110, 112.The power divider 105 may be coupled between the match network 114 andthe RF feed structure 106. Alternatively, the power divider may be apart of the match network 114, in which case the match network will havetwo outputs coupled to the RF feed structure 106—one corresponding toeach RF coil 110, 112. The power divider is discussed in more detailbelow in accordance with the embodiments illustrated in FIG. 4.

The RF feed structure 106 couples the RF current from the power divider116 (or the match network 114 where the power divider is incorporatedtherein) to the respective RF coils. In some embodiments, the RF feedstructure 106 may be configured to provide the RF current to the RFcoils in a symmetric manner, such that the RF current is coupled to eachcoil in a geometrically symmetric configuration with respect to acentral axis of the RF coils, such as by a coaxial structure.

The reactor 100 generally includes the process chamber 104 having aconductive body (wall) 130 and a dielectric lid 120 (that togetherdefine a processing volume), a substrate support pedestal 116 disposedwithin the processing volume, the inductively coupled plasma apparatus102, and a controller 140. The wall 130 is typically coupled to anelectrical ground 134. In some embodiments, the support pedestal 116 mayprovide a cathode coupled through a matching network 124 to a biasingpower source 122. The biasing source 122 may illustratively be a sourceof up to 1000 W at a frequency of approximately 13.56 MHz that iscapable of producing either continuous or pulsed power, although otherfrequencies and powers may be provided as desired for particularapplications. In other embodiments, the source 122 may be a DC or pulsedDC source.

In some embodiments, a link (not shown) may be provided to couple the RFpower supply 108 and the biasing source 122 to facilitate synchronizingthe operation of one source to the other. Either RF source may be thelead, or master, RF generator, while the other generator follows, or isthe slave. The link may further facilitate operating the RF power supply108 and the biasing source 122 in perfect synchronization, or in adesired offset, or phase difference. The phase control may be providedby circuitry disposed within either or both of the RF source or withinthe link between the RF sources. This phase control between the sourceand bias RF generators (e.g., 108, 122) may be provided and controlledindependent of the phase control over the RF current flowing in theplurality of RF coils coupled to the RF power supply 108. Furtherdetails regarding phase control between the source and bias RFgenerators may be found in commonly owned, U.S. patent application Ser.No. 12/465,319, filed May 13, 2009 by S. Banna, et al., and entitled,“METHOD AND APPARATUS FOR PULSED PLASMA PROCESSING USING A TIME RESOLVEDTUNING SCHEME FOR RF POWER DELIVERY,” which is hereby incorporated byreference in its entirety.

In some embodiments, the dielectric lid 120 may be substantially flat.Other modifications of the chamber 104 may have other types of lids suchas, for example, a dome-shaped lid or other shapes. The inductivelycoupled plasma apparatus 102 is typically disposed above the lid 120 andis configured to inductively couple RF power into the process chamber104. The inductively coupled plasma apparatus 102 includes the first andsecond coils 110, 112, disposed above the dielectric lid 120. Therelative position, ratio of diameters of each coil, and/or the number ofturns in each coil can each be adjusted as desired to control, forexample, the profile or density of the plasma being formed viacontrolling the inductance on each coil. Each of the first and secondcoils 110, 112 is coupled through the matching network 114 via the RFfeed structure 106, to the RF power supply 108. The RF power supply 108may illustratively be capable of producing up to 4000 W at a tunablefrequency in a range from 50 kHz to 13.56 MHz, although otherfrequencies and powers may be provided as desired for particularapplications.

The first and second RF coils 110, 112 can be configured such that thephase of the RF current flowing through the first RF coil can be out ofphase with respect to the phase of the RF current flowing through the RFsecond RF coil. As used herein, the term “out of phase” can beunderstood to mean that the RF current flowing through the first RF coilis flowing in an opposite direction to the RF current flowing throughthe second RF coil, or that the phase of the RF current flowing throughthe first RF coil is shifted with respect to the RF current flowingthrough the second RF coil.

For example, in conventional apparatus, both RF coils are typicallywound in the same direction. As such, the RF current is flowing in thesame direction in both coils, either clockwise or counterclockwise. Thesame direction of the winding dictates that the RF current flowing inthe two RF coils are always in phase. In the present invention, theinventors have examined providing RF current out of phase between thetwo coils by either external means or by physically winding one of thecoils in the opposite direction, thus altering the original phase. Bycontrolling the phase between the coils the inventors have discoveredthe ability to reduce and eliminate non-uniform etch results, such asthe M-shape etch pattern, and furthermore to control the processing(such as etch rate) pattern from center high, to edge high or to a flatand uniform processing pattern. By providing out of phase RF currentbetween the coils and by controlling the current ratio between the innerand outer coil the inventors have provided an apparatus that facilitatescontrol over the processing pattern to achieve improved uniformityacross the substrate.

By providing out of phase RF current between the coils, the apparatusreverses the destructive interference between the electromagnetic fieldsgenerated by each coil to be constructive, and, therefore, the typicalconstructive electric field plasma properties within the reactor may besimilarly reversed. For example, the present apparatus may be configuredto increase the electric field proximate each of the first and secondcoils and decrease the electric field between the coils by providing outof phase RF current flowing along the first and second coils. In someembodiments, such as where the RF current in each of the coils iscompletely out of phase (e.g., reverse current flow or 180 phasedifference) the electric fields may be maximized (or localized)proximate each of the first and second coils and minimized (or null)between the coils due to destructive interference between opposingelectric fields. The inventors have discovered that a plasma formedusing such a coil configuration can advantageously have an improved,e.g., a more uniform, electric field distribution and that components ofthe plasma may diffuse into the null region of the electric field toprovide a more uniform plasma.

In some embodiments, the direction of the RF current flowing througheach coil can be controlled by the direction in which the coils arewound. For example, as illustrated in FIG. 2, the first RF coil 110 canbe wound in a first direction 202 and the second RF coil 112 can bewound in a second direction 204 which is opposite the first direction202. Accordingly, although the phase of the RF signal provided by the RFpower supply 108 is unaltered, the opposing winding directions 202, 204of the first and second RF coils 110, 112 cause the RF current to be outof phase, e.g., to flow in opposite directions.

In some embodiments, a power divider, such as a dividing capacitor, maybe provided between the RF feed structure 106 to control the relativequantity of RF power provided by the RF power supply 108 to therespective first and second coils. For example, as shown in FIG. 1, apower divider 105 may be disposed in the line coupling the RF feedstructure 106 to the RF power supply 108 for controlling the amount ofRF power provided to each coil (thereby facilitating control of plasmacharacteristics in zones corresponding to the first and second coils).In some embodiments, the power divider 105 may be incorporated into thematch network 114. In some embodiments, after the power divider 105, RFcurrent flows to flows to the RF feed structure 106 where it isdistributed to the first and second RF coils 110, 112. Alternatively,the split RF current may be fed directly to each of the respective firstand second RF coils.

By adjusting the power ratio in combination with the phase of the RFsignal flowing through each of the first and second coils, the inventorshave discovered that undesired processing non-uniformities (such as theM-shape etch profile of a substrate surface) may be controlled. Forexample, FIGS. 3A-B illustratively depict graphs of etch rate profilesgenerated using conventional apparatus and an embodiment of theinventive apparatus as disclosed herein. These graphs illustrativelydepict data from actual tests and observations performed by theinventors. FIG. 3A depicts an etch rate profile graph of the etch rate(axis 310) radially along a substrate surface (axis 312) for a pluralityof power ratios between the first and second coils in a conventionalapparatus (plots 302A, 304A and 306A). While some control over the etchrate profile can be achieved by adjusting the power ratio in theconventional apparatus, as shown in FIG. 3A, the inventors havediscovered that any adjustment of the power ratio still results ininadequate overall uniformity, and in particular, poor edge profiletenability (e.g., each power ratio provides a limited effect at the edgeof the etch profile).

In contrast, FIG. 3B depicts an etch rate profile graph of the etch rate(axis 310) radially along a substrate surface (axis 312) for a pluralityof the same power ratios between the first and second coils in anapparatus in accordance with embodiments of the present invention havingthe RF current flowing through the first and second RF coils 180 degreesout of phase (plots 302B, 304B and 306B). Specifically, by making thesame power ratio adjustments in the inventive apparatus as shown in FIG.3B, the inventors have discovered that a significantly greater degree ofuniformity control can be achieved. In addition, greatly improved edgeprofile tunability can be also achieved. As can be seen from the graphin FIG. 3B, the inventive apparatus can provide a substantially uniformetch rate profile by tuning the power ratio (e.g., 304B) and can alsoprovide a significantly greater edge profile tunability as compared to aconventional apparatus. For example, by controlling the power ratio in achamber configured to have RF current flowing through the two RF coilsout of phase, the uniformity profile can be controlled to provide centerhigh and edge low etch rates, substantially flat etch rates, or centerlow and edge high etch rates. As these results are due to the plasmauniformity, such control is also transferrable to other processes orresults (such as plasma treatment, deposition, annealing, or the like)where plasma uniformity provides control over such processes or results.

Embodiments of an exemplary RF feed structure 106 that may be utilizedin combination with the out of phase RF coil apparatus disclosed hereinare described below and depicted in further detail in FIGS. 4A-B.Further details regarding the exemplary RF feed structure may be foundin U.S. Patent Application Ser. No. 61/254,838, filed on Oct. 26, 2009,by Z. Chen, et al., and entitled “RF FEED STRUCTURE FOR PLASMAPROCESSING,” which is hereby incorporated by reference in its entirety.For example, FIGS. 4A-B depicts the RF feed structure 106 in accordancewith some embodiments of the present invention. As depicted in FIG. 4A,the RF feed structure 106 may include a first RF feed 402 and a secondRF feed 404 coaxially disposed with respect to the first RF feed 402.The first RF feed 402 is electrically insulated from the second RF feed404. In some embodiments, and as illustrated, the second RF feed 404 iscoaxially disposed about the first RF feed 402, for example, alongcentral axis 401. The first and second RF feeds 402, 404 may be formedof any suitable conducting material for coupling RF power to RF coils.Exemplary conducting materials may include copper, aluminum, alloysthereof, or the like. The first and second RF feeds 402, 404 may beelectrically insulated by one or more insulating materials, such as air,a fluoropolymer (such as Teflon®), polyethylene, or the like.

The first RF feed 402 and the second RF feed 404 are each coupled todifferent ones of the first or second RF coils 110, 112. In someembodiments, the first RF feed 402 may be coupled to the first RF coil110. The first RF feed 402 may include one or more of a conductive wire,cable, bar, tube, or other suitable conductive element for coupling RFpower. In some embodiments, the cross section of the first RF feed 402may be substantially circular. The first RF feed 402 may include a firstend 406 and a second end 407. The second end 407 may be coupled to thematch network 114 (as shown) or to a power divider (as shown in FIG. 1).For example, as depicted in FIG. 4A, the match network 114 may include apower divider 430 having two outputs 432, 434. The second end 407 of thefirst RF feed 402 may be coupled to one of the two outputs of the matchnetwork 114 (e.g., 432).

The first end 406 of the first RF feed 402 may be coupled to the firstcoil 110. The first end 406 of the first RF feed 402 may be coupled tothe first coil 110 directly, or via some intervening supportingstructure (a base 408 is shown in FIG. 4A). The base 408 may be acircular or other shape and includes symmetrically arranged couplingpoints for coupling the first coil 110 thereto. For example, in FIG. 4A,two terminals 428 are shown disposed on opposite sides of the base 408for coupling to two portions of the first RF coil via, for example,screws 429 (although any suitable coupling may be provided, such asclamps, welding, or the like).

In some embodiments, and as discussed further below in relation to FIGS.5A-B, the first RF coil 110 (and/or the second RF coil 112) may comprisea plurality of interlineated and symmetrically arranged stacked coils(e.g., two or more). For example, the first RF coil 110 may comprise aplurality of conductors that are wound into a coil, with each conductoroccupying the same cylindrical plane. Each interlineated, stacked coilmay further have a leg 410 extending inwardly therefrom towards acentral axis of the coil. In some embodiments, each leg extends radiallyinward from the coil towards the central axis of the coil. Each leg 410may be symmetrically arranged about the base 408 and/or the first RFfeed 402 with respect to each other (for example two legs 180 degreesapart, three legs 120 degrees apart, four legs 90 degrees apart, and thelike). In some embodiments, each leg 410 may be a portion of arespective RF coil conductor that extends inward to make electricalcontact with the first RF feed 402. In some embodiments, the first RFcoil 110 may include a plurality of conductors each having a leg 410that extends inwardly from the coil to couple to the base 408 atrespective ones of the symmetrically arranged coupling points (e.g.,terminals 428).

The second RF feed 404 may be a conductive tube 403 coaxially disposedabout the first RF feed 402. The second RF feed 404 may further includea first end 412 proximate the first and second RF coils 110, 112 and asecond end 414 opposite the first end 412. In some embodiments, thesecond RF coil 112 may be coupled to the second RF feed 404 at the firstend 412 via a flange 416, or alternatively, directly to the second RFfeed 404 (not shown). The flange 416 may be circular or other in shapeand is coaxially disposed about the second RF feed 404. The flange 416may further include symmetrically arranged coupling points to couple thesecond RF coil 112 thereto. For example, in FIG. 4A, two terminals 426are shown disposed on opposite sides of the second RF feed 404 forcoupling to two portions of the second RF coil 112 via, for example,screws 427 (although any suitable coupling may be provided, such asdescribed above with respect to terminals 428).

Like the first coil 110, and also discussed further below in relation toFIGS. 5A-B, the second RF coil 112 may comprise a plurality ofinterlineated and symmetrically arranged stacked coils. Each stackedcoil may have a leg 418 extending therefrom for coupling to the flange416 at a respective one of the symmetrically arranged coupling points.Accordingly, each leg 418 may be symmetrically arranged about the flange216 and/or the second RF feed 404.

The second end 414 of the second RF feed 404 may be coupled to the matchnetwork 114 (as shown) or to a power divider (as shown in FIG. 1). Forexample, as depicted in FIG. 4A, the match network 114 includes a powerdivider 430 having two outputs 432, 434. The second end 414 of thesecond RF feed 404 may be coupled to one of the two outputs of the matchnetwork 114 (e.g., 434). The second end 414 of the second RF feed 404may be coupled to the match network 114 via a conductive element 420(such as a conductive strap). In some embodiments, the first and secondends 412, 414 of the second RF feed 404 may be separated by a length 422sufficient to limit the effects of any magnetic field asymmetry that maybe caused by the conductive element 420. The required length may dependupon the RF power intended to be used in the process chamber 104, withmore power supplied requiring a greater length. In some embodiments, thelength 422 may be between about 2 to about 8 inches (about 5 to about 20cm). In some embodiments, the length is such that a magnetic fieldformed by flowing RF current through the first and second RF feeds hassubstantially no effect on the symmetry of an electric field formed byflowing RF current through the first and second coils 110, 112.

In some embodiments, and as illustrated in FIG. 4B, the conductiveelement 420 may be replaced with a disk 424. The disk 424 may befabricated from the same kinds of materials as the second RF feed 404and may be the same or different material as the second RF feed 404. Thedisk 424 may be coupled to the second RF feed 404 proximate the secondend 414 thereof. The disk 424 may be an integral part of the second RFfeed 404 (as shown), or alternatively may be coupled to the second RFfeed 404, by any suitable means that provides a robust electricalconnection therebetween, including but not limited to bolting, welding,press fit of a lip or extension of the disk about the second RF feed404, or the like. The disk 424 may be coaxially disposed about thesecond RF feed 404. The disk 424 may be coupled to the match network 114or to a power divider in any suitable manner, such as via a conductivestrap or the like. The disk 424 advantageously provides an electricshield that lessens or eliminates any magnetic field asymmetry due tothe offset outputs from the match network 114 (or from the powerdivider). Accordingly, when a disk 424 is utilized for coupling RFpower, the length 422 of the second RF feed 204 may be shorter than whenthe conductive element 420 is coupled directly to the second RF feed404. In such embodiments, the length 422 may be between about 1 to about6 inches (about 2 to about 15 cm).

FIGS. 5A-B depict a schematic top down view of the inductively coupledplasma apparatus 102 in accordance with some embodiments of the presentinvention. As discussed above, the first and second coils 110, 112 neednot be a singular continuous coil, and may each be a plurality (e.g.,two or more) of interlineated and symmetrically arranged stacked coilelements. Further, the second RF coil 112 may be coaxially disposed withrespect to the first RF coil 112. In some embodiments, the second RFcoil 112 is coaxially disposed about the first RF coil 112 as shown inFIGS. 5A-B.

In some embodiments, and illustrated in FIG. 5A, the first coil 110 mayinclude two interlineated and symmetrically arranged stacked first coilelements 502A, 502B and the second coil 112 includes four interlineatedand symmetrically arranged stacked second coil elements 508A, 508B,508C, and 508D. The first coil elements 502A, 502B may further includelegs 504A, 504B extending inwardly therefrom and coupled to the first RFfeed 402. The legs 504A, 504B are substantially equivalent to the legs410 discussed above. The legs 504A, 504B are arranged symmetricallyabout the first RF feed 402 (e.g., they are opposing each other).Typically, RF current may flow from the first RF feed 402 through thelegs 502A, 502B into the first coil elements 504A, 504B and ultimatelyto grounding posts 506A, 506B coupled respectively to the terminal endsof the first coil elements 502A, 502B. To preserve symmetry, forexample, such as electric field symmetry in the first and second coils110, 112, the ground posts 506A, 506B may be disposed about the first RFfeed structure 402 in a substantially similar symmetrical orientation asthe legs 502A, 502B. For example, and as illustrated in FIG. 5A, thegrounding posts 506A, 506B are disposed in-line with the legs 502A,502B.

Similar to the first coil elements, the second coil elements 508A, 508B,508C, and 508D may further include legs 510A, 510B, 510C, and 510Dextending therefrom and coupled to the second RF feed 204. The legs510A, 510B, 510C, and 510D are substantially equivalent to the legs 418discussed above. The legs 510A, 510B, 510C, and 510D are arrangedsymmetrically about the second RF feed 404. Typically, RF current mayflow from the second RF feed 404 through the legs 510A, 510B, 510C, and510D into the second coil elements 508A, 508B, 508C, and 508Drespectively and ultimately to grounding posts 512A, 512B, 512C, and512D coupled respectively to the terminal ends of the second coilelements 508A, 508B, 508C, and 508D. To preserve symmetry, for example,such as electric field symmetry in the first and second coils 110, 112,the ground posts 512A, 512B, 512C, and 512D may be disposed about thefirst RF feed structure 402 in a substantially similar symmetricalorientation as the legs 510A, 510B, 510C, and 510D. For example, and asillustrated in FIG. 5A, the grounding posts 512A, 512B, 512C, and 512Dare disposed in-line with the legs 510A, 510B, 510C, and 510D,respectively.

In some embodiments, and as illustrated in FIG. 5A, the legs/groundingposts of the first coil 110 may oriented at an angle with respect to thelegs/grounding posts of the second coil 112. However, this is merelyexemplary and it is contemplated that any symmetrical orientation may beutilized, such as the legs/ground posts of the first coil 110 disposedin-line with the legs/grounding posts of the second coil 112.

In some embodiments, and illustrated in FIG. 5B, the first coil 110 mayinclude four interlineated and symmetrically arranged stacked first coilelements 502A, 502B, 502C, and 502D. Like the first coil elements 502A,502B, the additional first coil elements 502C, 502D may further includelegs 504C, 504D extending therefrom and coupled to the first RF feed402. The legs 504C, 504D are substantially equivalent to the legs 410discussed above. The legs 504A, 504B, 504C, and 504D are arrangedsymmetrically about the first RF feed 402. Like the first coil elements502A, 502B, the first coil elements 502C, 502D terminate at groundingposts 506C, 506D disposed in-line with legs 504C, 504D. To preservesymmetry, for example, such as electric field symmetry in the first andsecond coils 110, 112, the ground posts 506A, 506B, 506C, and 506D maybe disposed about the first RF feed structure 402 in a substantiallysimilar symmetrical orientation as the legs 502A, 502B, 502C, and 502D.For example, and as illustrated in FIG. 5B, the grounding posts 506A,506B, 506C, and 506D are disposed in-line with the legs 502A, 502B,502C, and 502D, respectively. The second coil elements 508A, 508B, 508C,and 508D and all components (e.g., legs/grounding posts) thereof are thesame in FIG. 5B as in FIG. 5A and described above.

In some embodiments, and as illustrated in FIG. 5B, the legs/groundingposts of the first coil 110 are oriented at an angle with respect to thelegs/grounding posts of the second coil 112. However, this is merelyexemplary and it is contemplated that any symmetrical orientation may beutilized, such as the legs/ground posts of the first coil 110 disposedin-line with the legs/grounding posts of the second coil 112.

Although described above using examples of two or four stacked elementsin each coil, it is contemplated that any number of coil elements can beutilized with either or both of the first and second coils 110, 112,such as three, six, or any suitable number and arrangement thatpreserves symmetry about the first and second RF feeds 402, 404. Forexample, three coil elements may be provided in a coil each rotated 120degrees with respect to an adjacent coil element.

The embodiments of the first and second coils 110, 112 depicted in FIGS.5A-B can be utilized with any of the embodiments for altering the phasebetween the first and second coils as described above. For example, eachof the first coil elements 502 can be wound in an opposite direction toeach of the second coil elements 508 such that RF current flowingthrough the first coil elements is out of phase with RF current flowingthrough the second coil elements. Alternatively, when a phase shifter isused, the first and second coil elements 502, 508 can be wound in thesame direction or in an opposite direction.

Returning to FIG. 1, optionally, one or more electrodes (not shown) maybe electrically coupled to one of the first or second coils 110, 112,such as the first coil 110. The one or more electrodes may be twoelectrodes disposed between the first coil 110 and the second coil 112and proximate the dielectric lid 120. Each electrode may be electricallycoupled to either the first coil 110 or the second coil 112, and RFpower may be provided to the one or more electrodes via the RF powersupply 108 via the inductive coil to which they are coupled (e.g., thefirst coil 110 or the second coil 112).

In some embodiments, the one or more electrodes may be movably coupledto one of the one or more inductive coils to facilitate the relativepositioning of the one or more electrodes with respect to the dielectriclid 120 and/or with respect to each other. For example, one or morepositioning mechanisms may be coupled to one or more of the electrodesto control the position thereof. The positioning mechanisms may be anysuitable device, manual or automated, that can facilitate thepositioning of the one or more electrodes as desired, such as devicesincluding lead screws, linear bearings, stepper motors, wedges, or thelike. The electrical connectors coupling the one or more electrodes to aparticular inductive coil may be flexible to facilitate such relativemovement. For example, in some embodiments, the electrical connector mayinclude one or more flexible mechanisms, such as a braided wire or otherconductor. A more detailed description of the electrodes and theirutilization in plasma processing apparatus can be found in U.S. patentapplication Ser. No. 12/182,342, filed Jul. 30, 2008, titled “FieldEnhanced Inductively Coupled Plasma (FE-ICP) Reactor,” which is hereinincorporated by reference in its entirety.

A heater element 121 may be disposed atop the dielectric lid 120 tofacilitate heating the interior of the process chamber 104. The heaterelement 121 may be disposed between the dielectric lid 120 and the firstand second coils 110, 112. In some embodiments. the heater element 121may include a resistive heating element and may be coupled to a powersupply 123, such as an AC power supply, configured to provide sufficientenergy to control the temperature of the heater element 121 to bebetween about 50 to about 100 degrees Celsius. In some embodiments, theheater element 121 may be an open break heater. In some embodiments, theheater element 121 may comprise a no break heater, such as an annularelement, thereby facilitating uniform plasma formation within theprocess chamber 104.

During operation, a substrate 114 (such as a semiconductor wafer orother substrate suitable for plasma processing) may be placed on thepedestal 116 and process gases may be supplied from a gas panel 138through entry ports 126 to form a gaseous mixture 150 within the processchamber 104. The gaseous mixture 150 may be ignited into a plasma 155 inthe process chamber 104 by applying power from the plasma source 108 tothe first and second coils 110, 112 and optionally, the one or moreelectrodes (not shown). In some embodiments, power from the bias source122 may be also provided to the pedestal 116. The pressure within theinterior of the chamber 104 may be controlled using a throttle valve 127and a vacuum pump 136. The temperature of the chamber wall 130 may becontrolled using liquid-containing conduits (not shown) that run throughthe wall 130.

The temperature of the wafer 114 may be controlled by stabilizing atemperature of the support pedestal 116. In one embodiment, helium gasfrom a gas source 148 may be provided via a gas conduit 149 to channelsdefined between the backside of the wafer 114 and grooves (not shown)disposed in the pedestal surface. The helium gas is used to facilitateheat transfer between the pedestal 116 and the wafer 114. Duringprocessing, the pedestal 116 may be heated by a resistive heater (notshown) within the pedestal to a steady state temperature and the heliumgas may facilitate uniform heating of the wafer 114. Using such thermalcontrol, the wafer 114 may illustratively be maintained at a temperatureof between 0 and 500 degrees Celsius.

The controller 140 comprises a central processing unit (CPU) 144, amemory 142, and support circuits 146 for the CPU 144 and facilitatescontrol of the components of the reactor 100 and, as such, of methods offorming a plasma, such as discussed herein. The controller 140 may beone of any form of general-purpose computer processor that can be usedin an industrial setting for controlling various chambers andsub-processors. The memory, or computer-readable medium, 142 of the CPU144 may be one or more of readily available memory such as random accessmemory (RAM), read only memory (ROM), floppy disk, hard disk, or anyother form of digital storage, local or remote. The support circuits 446are coupled to the CPU 144 for supporting the processor in aconventional manner. These circuits include cache, power supplies, clockcircuits, input/output circuitry and subsystems, and the like. Theinventive method may be stored in the memory 142 as software routinethat may be executed or invoked to control the operation of the reactor100 in the manner described above. The software routine may also bestored and/or executed by a second CPU (not shown) that is remotelylocated from the hardware being controlled by the CPU 144.

FIG. 6 depicts a flow chart of a method for forming a plasma inaccordance with some embodiments of the present invention. The method600 is described below in accordance with embodiments of the inventionillustrated in FIGS. 1-3, however, the method 600 can be applied withany embodiments of the invention described herein.

The method 600 begins at 602 by providing an RF signal through a firstRF coil, such as the first RF coil 110 (although the “first RF coil” ofthe method 600 may be either of the RF coils discussed above). The RFsignal may be provided at any suitable frequency desired for aparticular application. Exemplary frequencies include but are notlimited to, a frequency of between about 100 kHz to about 60 MHz. The RFsignal may be provided at any suitable power, such as up to about 5000Watts.

At 604, the RF signal is provided through a second RF coil, e.g., thesecond RF coil 112, coaxially disposed with respect to the first RF coilsuch that the RF signal flows through the second coil out of phase withrespect to the flow of the RF signal through the first coil. Any of theabove embodiments may be utilized to control the phase of the RF currentflowing through the first and second coils. For example, as discussedabove, to create an out of phase condition between the first and secondcoils, the first and second coils can be wound in opposite directions,e.g., the first and second directions 202, 204 as illustrated in FIG. 2.Alternatively or in combination, a phase shifter, such as phase shifter302, or blocking capacitors 302, 304, can be utilized to shift the phaseof the RF current flowing through the first and/or second RF coils suchthat the RF current flowing through the first RF coil is out of phasewith the RF current flowing through the second RF coil. In someembodiments, the phase shifter or blocking capacitor may shift the phasesuch that the RF current flowing through the first RF coil is about 180degrees out of phase with the RF current flowing through the second RFcoil. However, the RF current need not be about 180 degrees out ofphase, and in some embodiments, the phase may be between about 0 toabout +/−180 degrees out of phase.

At 606, a plasma, such as the plasma 155, may be formed by coupling theRF signal provided by the first and second RF coils to a process gas,such as the gaseous mixture 150, disposed in a process chamber. Theprocess gas may include any suitable process gas for forming a plasma.In some embodiments, the RF signal may be provided at an equal powersetting to each of the first and second RF coils. In some embodiments,the RF signal may be provided at a fixed or an adjustable power ratio ofbetween about 1:0 to about 0:1 between the first and second RF coils.The plasma may be maintained for a desired period of time using the sameor different settings of the RF current ratio and/or the phasedifference of the RF current flowing through the first and second RFcoils.

Thus, methods and apparatus for plasma processing are provided herein.The inventive methods and plasma processing apparatus advantageousreduces additive electric field properties between adjacent plasma coilsin multi-coil plasma apparatus. Accordingly, a plasma formed utilizingthe inventive plasma apparatus has an improved electric fielddistribution, and can be utilized to produce a smoother etch surface.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

1. A plasma processing apparatus, comprising: a process chamber havingan interior processing volume; a first RF coil disposed proximate theprocess chamber to couple RF energy into the processing volume; a secondRF coil disposed proximate the process chamber to couple RF energy intothe processing volume, the second RF coil disposed coaxially withrespect to the first RF coil; and a phase shifter coupled to either thefirst or second RF coil to shift the phase of the RF current flowingtherethrough such that that RF current flowing through the first RF coilis out of phase with RF current flowing through the second RF coil. 2.The apparatus of claim 1, wherein the phase shifter shifts the phase ofthe RF current such that the RF current flowing through the first RFcoil is about 180 degrees out of phase with RF current flowing throughthe RF second coil.
 3. The apparatus of claim 1, wherein the first RFcoil and the second RF coil are wound in the same direction.
 4. Theapparatus of claim 1, wherein the first RF coil is wound in a firstdirection and wherein the second RF coil is wound in a second directionopposite the first direction.
 5. A plasma processing apparatus,comprising: a process chamber having an interior processing volume; afirst RF coil disposed proximate the process chamber to couple RF energyinto the processing volume; a second RF coil disposed proximate theprocess chamber to couple RF energy into the processing volume, thesecond RF coil disposed coaxially with respect to the first RF coil; andone or more blocking capacitors coupled to at least one or the first orsecond RF coil to shift the phase of the RF current flowing therethroughsuch that RF current that flows through the first RF coil is out ofphase with RF current that flows through the second RF coil.
 6. Theapparatus of claim 5, wherein the one or more blocking capacitors shiftthe phase of the RF current such that the RF current flowing through thefirst RF coil is about 180 degrees out of phase with RF current flowingthrough the RF second coil.
 7. The apparatus of claim 5, wherein thefirst RF coil and the second RF coil are wound in the same direction. 8.The apparatus of claim 5, wherein the first RF coil is wound in a firstdirection and wherein the second RF coil is wound in a second directionopposite the first direction.
 9. A method of forming a plasma,comprising: providing an RF signal through a first RF coil; providingthe RF signal through a second RF coil coaxially disposed with respectto the first RF coil such that the RF signal flows through the secondcoil out of phase with respect to the flow of the RF signal through thefirst coil, wherein at least one of a phase shifter or one or moreblocking capacitors are used to shift the phase of the RF signal suchthat the RF signal flowing through the first RF coil is out of phasewith RF signal flowing through the second RF coil; and forming a plasmaby coupling the RF signal provided by the first and second RF coils to aprocess gas disposed in a process chamber.
 10. The method of claim 9,wherein the RF signal flowing through the first and second RF coils areabout 180 degrees out of phase.
 11. The method of claim 9, wherein thefirst RF coil and the second RF coil are wound in the same direction.12. The method of claim 9, wherein the first RF coil is wound in a firstdirection and wherein the second RF coil is wound in a second directionopposite the first direction.